Structure, Chemical And Photochemical Reactivity And Biological Activity Of Some Ruthenium Amine Nitrosyl Complexes

Through spectroscopic (X-ray, Infrared, 1H-NMR, EPR, UV-vis) and electrochemical (cyclic voltammetry, differential pulse polarography) data and quantum mechanical calculations, the formulation [Ru(II)NO+] was attributed to a series of new ruthenium(II) amine compounds. A remarkable stability of the Ru(II) relative to Ru(III) was observed upon coordination to NO. The presence of nitrosyl in the coordination sphere results in dramatic implications in the lability, acidity and redox properties of the ligand trans to NO. These effects are higher than expected just on the basis of one unity increment in the metal center charge. Based on molecular orbital (MO) analysis and on reduction product analysis, the site of the reduction [Ru(NO)]3+ +e- → [Ru(NO)]2+ was assigned to the NO ligand. The dissociation of the coordinated NO0 is dependent on the trans effect and trans influence of the trans ligand L. Irradiation of the nitrosyl complexes with 300-350 nm light results in NO aquation and formation of the corresponding aquaruthenium(III) complex, i.e. S0010854502001777 Irradiation in the visible region (400-500 nm) did not result in any observable reaction in solution; however, at low temperature and in the solid state, evidence in favor of the formation of linkage isomers has been obtained. The hypotensive properties of trans[Ru(NO)(NH3)4(P(OC2 H5)3)](PF6)3 and trans -[Ru(NO)Cl(cyclam)](ClO4)2 have been demonstrated in mice and rats. © 2002 Elsevier Science B.V. All rights reserved.23601/02/155769Richter-Addo, G.B., Legzdins, P., (1992) Metal Nytrosyls, , (and references therein), Oxford University Press, New YorkBottomley, F., (1989) Reactions of Coordinated Ligands, 2. , P.S. Braterman (Ed.), (references therein), Plenum Press, New YorkEnemark, J.H., Feltham, R.D., (1974) Chem. 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4,4′-dithiodipyridine As A Bridging Ligand In Osmium And Ruthenium Complexes: The Electron Conductor Ability Of The -s-s- Bridge

The compounds [Ru(NH 3) 5(dtdp)](TFMS) 3, [Os(NH 3) 5(dtdp)](TFMS) 3, [(NH 3) 5Os(dtdp)Os(NH 3) 5](TFMS) 6, [(NH 3) 5Os(dtdp)Ru(NH 3) 5](TFMS) 3(PF 6) 2, and [(NH 3) 5Os(dtdp)Fe(CN) 5] (dtdp = 4,4′-dithiodipyridine, TFMS = trifluoromethane-sulfonate) have been synthesized and characterized by elemental analysis, cyclic voltammetry, electronic, vibrational, EPR, and 1H NMR spectroscopies. Changes in the electronic and voltammetric spectra of the ion complex [Os(NH 3) 5(dtdp)] 3+ as a function of the solution pH enable us to calculate the pK a for the [Os(NH 3) 5(dtdpH)] 4+ and [Os(NH 3) 5(dtdpH)] 3+ acids as 3.5 and 5.5, respectively. The comparison of the above pK a data with that for the free ligand (pK 1 = 4.8) provides evidence for the -S-S- bridge efficiency as an electron conductor between the two pyridine rings. The symmetric complex, [(NH 3) 5Os(dtdp)Os(NH 3) 5] 6+, is found to exist in two geometric forms, and the most abundant form (most probably trans) has a strong conductivity through the -S-S- bridge, as is shown by EPR, which finds it to have an S = 1 spin state with a spin-spin interaction parameter of 150-200 G both in the solid sate and in frozen solution. Further the NMR of the same complex shows a large displacement of unpaired spin into the π orbitals of the dttp ligand relative to that found in [Os(NH 3) 5(dtdp)] 3+. The comproportionation constant, K c = 2.0 × 10 5, for the equilibrium equation [Os IIOs II] + [Os IIIOs III] ⇌ 2[Os IIOs III] and the near-infrared band energy for the mixed-valence species (MMCT), [(NH 3) 5Os(dtdp)Os(NH 3) 5] 5+ (λ MMCT = 1665 nm, ε = 3.5 × 10 3 M -1 cm -1, Δν̄ 1/2 = 3.7 × 10 3 cm -1, α = 0.13, and H AB = 7.8 × 10 2 cm -1), are quite indicative of strong electron delocalization between the two osmium centers. The electrochemical and spectroscopic data for the unsymmetrical binuclear complexes [(NH 3) 5Os III(dtdp)Ru II(NH 3) 5] 5+ (λ MMCT = 965 nm, ε = 2.2 × 10 2 M -1 cm -1, Δν̄ 1/2 = 3.0 × 10 3 cm -1, and H AB = 2.2 × 10 2 cm -1) and [(NH 3) 5Os III(dtdp)Fe II(CN) 5] (λ MMCT = 790 nm, ε = 7.5 × 10 M -1 cm -1, Δν̄ 1/2 = 5.4 × 10 3 cm -1, and H AB = 2.0 × 10 2 cm -1) also suggest a considerable electron delocalization through the S-S bridge. 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